Status of the Indiana Bat, Myotis sodalis, in Pilot Knob Mine, Iron County, Missouri, 2008 Final Report to the United States Fish & Wildlife Service Pilot Knob National Wildlife Refuge 15 August 2008 William R. Elliott Missouri Department of Conservation Jim Kennedy Bat Conservation International 1 Status of the Indiana Bat, Myotis sodalis, in Pilot Knob Mine, Iron County, Missouri, 2008 Final Report to the United States Fish & Wildlife Service Pilot Knob National Wildlife Refuge 15 August 2008 William R. Elliott Missouri Department of Conservation Resource Science Division Cave Lab, Runge Conservation Nature Center P.O. Box 180 Jefferson City, MO 65102-0180 [email protected] 573-522-4115 ext 3194 Jim Kennedy Bat Conservation International P.O. Box 162603 Austin, TX 78716-2603 [email protected] 512-327-9721 ext 17 Cover photo: View of Pilot Knob from Fort Davidson, a Civil War battlefield. The cut in the top of the hill contains the major adits (entrances) to the mine. Photo by William R. Elliott. 2 Abstract On February 25-26, 2008 we conducted a bat census and reconnaissance in Pilot Knob Mine, Missouri, and its environs in cooperation with the US Fish & Wildlife Service, Missouri Department of Conservation and Bat Conservation International. Following a written plan with safety equipment, instruments, and cameras, we documented a total of 1,678 Indiana bats (Indiana myotis, Myotis sodalis) in the lower and upper portions of the mine. Thirteen adits were checked and GPS fixes were obtained, but only the four adits leading into the two main cavities contained bat clusters. We provide a review of all available documents and photographs, and new estimates of the bats in the mine. M. sodalis declined by 98%, from about 80,000-100,000 in 1958 to about 2,000 in 2008. Intruders may have affected the bats, but much of the decline probably was the result of a partial collapse of the lower mine in 1979, which may have killed many bats, followed by probable changes in airflow and the availability of habitat. Recom- mendations are provided for improved, cooperative management of the mine and Refuge. Introduction Pilot Knob Mine, Iron County, Missouri, became a National Wildlife Refuge in 1987 (Sweet 1988). Its focus is protection of critical habitat for the endangered Indiana myotis, Myotis sodalis, which hibernates there in substantial numbers. Despite the decline of Indiana bats in recent years, Pilot Knob Mine remains an important mating and swarming place, hibernaculum and refuge for several species of bats. This report presents the results of a census trip and reconnaissance of the mine on February 25-26, 2008. The authors obtained a permit from the US Fish & Wildlife Service (FWS) to survey the interior and environs of the mine for Indiana bats, after we provided a written safety plan and procedures (Appendix). The summit of Pilot Knob is geologically and geographically unique, providing a panoramic view of the surrounding area, which includes a Civil War battlefield, Fort Davidson, at the foot of the hill (Figures 1-3). The Knob is formed in Precambrian rhyolite, which is volcanic, and sedimentary tuff. It contained a rich iron ore body that was mined from about 1835 to about 1890 (Figures 4-6). Mining resumed for a time, ending between 1912 and 1920 (Litton 1855, Nason 1892, Crane 1912, USGS 1967, Kisvarsanyi 2001). Open pits remain near the top of the hill, but the underground portions of the mine were largely mined out near the end of the mining period, and some portions were collapsed by removing pillars. Bats may have begun using the mine long ago, but we presume that they encountered fewer disturbances after 1920. However, local youths have a long tradition of visiting the mine, although it has a reputation of being dangerous. This tradition continues today despite its federal Refuge status and a high perimeter fence. Review of Previous Studies An attached computer disk with many files has an Excel® spreadsheet (Pilot Knob Mine.xls) containing several worksheets of interest. The contents are provided on a computer disk to FWS: 2008 census Results of the in-mine counts, February 25, 2008 (Tables 1 and 4). GIS Pilot Knob Mine (pkm) adit UTM coordinates from GPS fixes (Table 2). 3 Calc A recalculation of LaVal and Clawson’s population estimates (Table 3). General A chronological list of 115 events, bat counts, harp-trap results, management actions, digital files and documents scanned from the Missouri Department of Conservation’s (MDC) files (Table 5). Myso Table 6 of in-mine counts, revised estimates, old harp-trap population estimates, and trapping rates for M. sodalis (Myso), and a graph (same as Figure 31). Trap Date Examination of the effect of early vs. later harp-trapping dates (see p. 8). Bat files List of scanned field data sheets and documents with bat results. Gate Cost of the 2001 bat gate built on the lower mine, since removed. On February 22, 1958, Richard Myers visited the mine with three young local men to photograph the hibernating Indiana myotis (Figures 7-12, Table 5). He visited the mine again on April 11 and December 27, 1958. In December the “Devil’s Icebox,” as the lower mine was called, contained about 80,000 M. sodalis by Myers’ estimate. We believe that this was a conservative estimate, based on a density of 220 bats/foot2 (Myers 1964, table 1, pp. 26-35). The February photograph (Figure 9) appears to have about 300 bats/foot2, which we estimated from the size of a man’s hand near the bats and counting bats in a frame. Myers also estimated at least 35,000 M. lucifugus in the mine. We concur with FWS that 100,000 may be a reasonable re- estimate for 1958, especially since the upper mine was not visited during Myers’ trips, but we know that it now harbors bats. In February, 1958, the interior of the mine appeared to be stable, with old stulls (tree trunks used as roof supports) mostly still in place. By December he noticed that boulders had shifted and there had been some rock falls in the entrance area and on the route to the hibernaculum. Myers last visited the mine in March, 1960. (R. Myers, pers. comm.) In 1975 Richard and Margaret LaVal from MDC began harp-trapping bats at the lower mine entrance, but they did not enter the mine, owing to its “dangerous” reputation. Richard Clawson soon joined their project, and they continued the effort until 1978 (Clawson and Titus 1988). Trapping usually was done in late September or early October during the fall mating swarm. The great majority of bats captured and released, usually over a two-hour period in two “bags,” were M. sodalis, with some M. lucifugus (little brown bat) and M. septentrionalis (northern bat). They were identified to species, most were sexed, and some were weighed and examined in detail. In a letter dated November 17, 1978 to Larry Visscher, FWS, Richard Laval reported, “…Because we know the hibernating population of Great Scott Cave, we can, if we assume bat activity at cave entrances is proportional to number hibernating in the cave, calculate the hibernating population of Pilot Knob by measuring the rate at which bats fly through the entrance on consecutive nights. Thus, on 14 and 19 October catch rates were 4.36 bats/min and 2.91 bats/min., respectively, at Great Scott. Meanwhile, on 12 and 21 October catch rates at Pilot Knob were 10.38 and 6.74, respectively. Using a mean (based on 4 years’ data) population at Great Scott, the calculated population at Pilot Knob is [between] 139000 and 135000, using the two sets of data. Thus these data support our contention that PKM is the world's largest hibernaculum for Indiana bats…” Harp trapping was done April 8, 17 and 18, 1979, with nothing unusual recorded, but on May 25, 1979 LaVal recorded in his notes, “A colossal collapse has occurred, blocking the two entrances used by bats. Cold air is blowing out of the rocks above the old main exit site; it appears a person could still get in, by climbing among 4 newly fallen giant boulders. The higher main entrance that was being used by nearly half the bats earlier this spring appears to be completely blocked. The entire south wall of the ‘Devil’s Icebox’ has collapsed, partially filling the icebox. Rock still standing looks very unstable. There are many new cracks in the rocks and earth along the trail to the top of the hill from the icebox. The third entrance not formerly used by bats (high up on the end of the icebox) is still open. We suspect foul play, but saw no evidence of same. Note, from 2000 on, a few bats emerging from remains of lower main entrance.” A federal agent was sent to investigate, but he reported no evidence of violations. After the collapse there were no harp-trapping trips until 1992. Figures 12, 19 and 20 show quarry conditions before and since the collapse. On September 16, 1986, a local 17-year-old boy was trapped and injured in the lower mine while exploring with a friend. After a two-day ordeal he was rescued by local responders and cavers from St. Louis (The Mountain Echo 1986, Kelly 1987). This incident, in which the youth nearly lost his life or his legs, prompted many to call for permanent closure of the mine. But its value as a bat refuge also was publicized. Within a year FWS received a donation of the mine and 90 acres from the Pilot Knob Ore Co.